1. Field of the Invention
The present invention relates generally to the field of level detection circuitry and in particular to circuitry for detecting the level of an input signal, such as a power supply voltage, which is also powered by the input signal.
2. Background of Related Art
Most electronic systems contain storage elements which have indeterminate states when the primary power source for the system is first applied or when the power source drops below some minimum operating level. Accordingly, it is often necessary to provide some means whereby the storage elements are set to a known state at initial power on or after a power drop. Such circuits are sometimes referred to as power on reset circuits.
One difficulty in implementing power on reset circuits is that such circuits must often be powered by the same voltage source that is monitored by the circuit. This can present a challenge, particularly if the circuit must ensure that the system is in a proper initial state at relatively low supply voltages. Furthermore, such reset circuits must operate reliably when the input supply voltage either has a very fast rise time or a slow rise time.
The present invention is capable of detecting input signals, such as power supply voltages, while being powered by such input signals. The input signal level is reliably and accurately detected and an output is provided to accommodate input signals having fast and slow rising inputs. These and other advantages of the present invention will be apparent to those skilled in the art upon a reading of the following Detailed Description of the Invention together with the drawings.